This invention relates to a coreless motor.
In recent years, there has been exploited a coreless motor using an iron-coreless rotor having one or more flat type coils bonded to an insulating substrate. The rotor of this type of motor is prepared by laminating flat spiral coils made of, for example conductive foils or made by printing, on a light insulating substrate formed of, for example, synthetic resin. Because no iron core is used, this motor is light as a whole and its inertial force is small. When, therefore, this rotor is used in a tape-driving motor of, for example, a tape recorder which requires such nature or property, a rotational rise of a capstan shaft at the time when the motor is started, and a tape stop at a prescribed position can be quickly and smoothly effected.
FIG. 2 shows a rotor R.sub.1 of a conventional DC commutator-motor wherein the numer n of pole members of a commutator S.sub.1 is 5 and the number 2p of magnetic pole members of a magnet stator M.sub.1 is 2. In FIG. 2, C.sub.11, C.sub.12 . . . C.sub.15 indicate models of sectorial loop coils and S.sub.11, S.sub.12 . . . S.sub.15 denote pole members of the commutator S.sub.1. The sectorial loop coils C.sub.11, C.sub.12 . . . C.sub.15 are arranged around a rotary shaft 11 in such a manner as to be mutually lapped into two layers and equidistantly spaced from each other and made flat. The wind-starting end of one of the lapped coils is connected in turn to the wind-terminating end of the other, and these connection points are connected to the pole members S.sub.11, S.sub.12 . . . S.sub.15 of the commutator S.sub.1, respectively. The rotor R.sub.1 is disposed in such a manner that the flat surface of its loop coil section is faced to the magnetic pole member surface of the magnet stator M.sub.1 having two magnetic pole members. The respective loop coils C.sub.11, C.sub.12 . . . C.sub.15 are so arranged that the angle .theta. of each loop coil flared toward itself from the center of the rotor is specified. That is to say, the angle .theta..sub.1 is set as follows from the relation with the number n of pole members of the commutator S.sub.1 and the number 2p of magnetic pole members of the magnet stator M.sub.1. ##EQU2## that is, .theta..sub.1 = 144.degree.
Let it be now assumed, in the case of the above-mentioned construction, that brushes contact the pole members S.sub.12 and S.sub.15 of the commutator S.sub.1, respectively, and current flows in the loop coils C.sub.11, C.sub.12 . . . C.sub.15 through said brushes. Then the directions in which current flows in the respective loop coils C.sub.11, C.sub.12 . . . C.sub.15 are as indicated by arrows. In this case, as seen from FIG. 2, at one (shown by A) of the lapped portions of the loop coils current flows in opposite directions to offset the resulting mutual electromagnetic forces. Accordingly, this lapped portion does not contribute to the generation of rotation force of the rotor, which constitutes one of the causes of decreasing the motor efficiency.